PROJECT SUMMARY/ABSTRACT Intrinsically disordered proteins (IDPs) are a ubiquitous class of proteins whose structural plasticity allows them to function as hubs in protein-protein interaction (PPI) and signaling networks. IDP PPIs are therefore tightly regulated, and aberrant IDP PPIs are associated with many disease states. As IDP folding and activity are dependent on the conformations induced by its native binding partners, small molecules that induce native-like IDP conformations are highly desirable for studying IDP function. However, complex IDP PPI interfaces are difficult targets for traditional small molecules. Instead, non-traditional approaches using stabilized ?-helical peptides, such as the hydrogen bond surrogate (HBS) approach developed in the Arora laboratory, are promising for creating small molecules that nucleate native-like IDP folding with both high affinity and high specificity. Thus, I hypothesize that HBS peptides can mimic key portions of IDP binding partners to nucleate IDP folding and competitively inhibit IDP PPIs in vitro and in vivo. The overall goal is to create HBS-derived artificial folders that induce IDPs to favor one fold over others. A classic IDP PPI example is the interaction of the general transcriptional coactivator p300 with the intrinsically disordered C-terminal transcription-activation domain of hypoxia-inducible factor 1 ? (HIF1? CTAD). This interaction is critical for hypoxia-inducible transcription, leading to the upregulation of many cancer-associated genes involved in angiogenesis, invasion, and proliferation. The Arora lab has shown that mimicry of a HIF1? CTAD helical fragment downregulates hypoxia-inducible transcription and decreases xenograft tumor size in mice. However, targeting p300 may impair its ability to interact with its numerous binding partners. In the current proposal, I propose to develop a complementary strategy to use HBS peptides to induce HIF1? CTAD folding and competitively inhibit the p300-HIF1? CTAD interaction. To achieve this goal, I will first design and synthesize HBS peptides that mimic a p300 helical fragment that interacts with HIF1? CTAD. I will evaluate HBS peptide binding affinity and specificity for HIF1? CTAD in vitro. I will then characterize the structures of HIF1? CTAD-HBS complexes to evaluate HBS peptide-induced folding of HIF1? CTAD. I will also evaluate HBS peptides? ability to modulate HIF1?-mediated transcription using cell-based assays. HBS peptides that induce native-like HIF1? CTAD folding with high affinity and specificity may serve as useful tools for studying HIF1? function and potential cancer therapeutic leads for HIF1? inhibition. This strategy for inducing IDP folding may also provide a specific application of a general approach to modulate IDP structures and activities using structured peptides.